The present invention relates to the field of integrated circuit substrates and packaging and more specifically to methods and devices which improve the reliability of conductive ball joints, especially when mounted on a printed circuit board.
Integrated circuits (ICs) or “chips” are becoming denser and are providing higher performance and functionality per unit area. Many ICs have hundreds of pads that will interface with the printed circuit board (PCB). The packaging for the IC seals the chip and connects the pads of the chip to the balls, pins, leads, or other electrical contacts of the package.
It is important that the IC package is relatively low in cost. Previous generations of IC packages were ceramic or included materials or used techniques that increased the cost of the packaging. It is also important that the IC packaging sufficiently protects the chip and provides the necessary number of electrical connections, and provides this function using as small a package size as possible. A package with a smaller footprint takes up less PCB space and more ICs can be mounted on a single PCB.
Another important consideration in IC packaging is reliability. One concern is that when an IC package is soldered or otherwise electrically connected to the PCB, the IC package should be reliably electrically connected to the PCB, or else over time open circuit or no connection failures will result. Because temperature cycling occurs when the IC heats up during operation, and cools off when not in operation, the solder connections between the IC and the PCB may be subjected to shear and stress forces as the package expands and contracts. The solder balls may work harden and then fracture. Consequently, cracks in the solder balls will cause open circuits, and ultimately system failure.
Therefore, as can be appreciated, methods and devices are needed to provide IC packaging with a lower cost, smaller package size, and better reliability. Specifically, there is a need to design integrated circuit packages which enhance solder ball reliability and longevity while maintain the small size of the package and large amount of contacts between the die and the PCB.